Recovery of silver from scrap films



soluble form without first re-ccnverting the re The dissolution was materially faster in the more duced silver to silver halide. concentrated solutions and it was found that it According to this invention the silver is discould be further hastened by warming the bath solved from the waste photographic film by treatand/or mechanical stirring. Mossy zinc was ing with a solution of thiourea. While the nature then added to the silver solutions and the silver of the chemical reaction taking place is not soon precipitated on the zinc surfaces. thoroughly understood it has been found that the The invention is not limited to the specific emsilver is dissolved by. the thiourea solution from bodiments described above. Many changes and which it may be recovered by known means. modifications may be made and the invention In carrying out the process waste photographic embodied in widely different forms. Molecular film is immersedin an aqueous solution of thiosilver can be recovered by the process described urea at either room or elevated temperatures. from moving picture film or any other scrap The conversion of the silver into soluble form is photographic film or plate. found to be complete approximately when the The present invention is limited solely by the black portions of the exposed film disappear and claims attached hereto as part ofthe present the him is rendered white or transparent. The specification. concentration of the thiourea is not at all critical. What is claimed is: Very satisfactory results have been obtained with 1. A process for treating waste photographic Patented Dec. 8, 1942 i 2,304,427.

UNITED STATES PATENT. OFFICE 2,304,421 ascovsnr or smvnn mom sonar FILMS Robert L. Sibley, Nitro, W. Va; assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. .F Appl i cation ri 5, 1941, Serial No. 396,741

'fliis invention relates to the treatment of subject to many variables and can not be stated photographic films and the like for the recovery definitely it was found that merely standing at of silver. r room temperature for one to two days was sufli- The principal fieature or the invention consists cient to complete the dissolution of the silver in in theconversion of the silver directly into a 5 the'dilute (2 and 3 percent) thiourea solutions.

from three to ten percent thiourea by weight but films and th k fo he ry of silver whi solutions of diflerent strength may be used where comprises converting the silver into soluble form convenient. However, the time consumed in the by treating with a solution consisting of thiourea dissolution is noticeably longer in the case of in water. dilute thiourea solutions so that it is preferred to 2. A process for treating waste photographic use solutions which approach saturation. films and the like for the recovery of silver which The silver may be recovered from solution in comprises converting the silver into soluble form which it exists probably in some form of complex by heating with a solution consisting of at least combination with the thiourea, by deposition on a two percent thiourea in water. suitable metal, preferably mossy zinc. Obviously 3. A process for treating waste photographic other methods of precipitating the silver may be film and the like for the recovery of silver which used. Thus, the silver may be removed in the comprises converting the silver into soluble form form of sulfide or recovered direct from the thioby treating with a solution consisting of at least urea solutionby electrolysis. two percent thiourea in water and precipitating As specific embodiments of the invention, the silver on mossy zinc. aqueous solutions of 2, 3, 5 and 10 percent by 4. A process for treating photographic films weight thiourea were prepared and waste photo- 40 and the like for the recovery of silver which com: graphic film immersed therein. The black silver prises converting the silver into soluble form by deposit soon began to disappear and when the treating with an aqueous ,thiourea solution and film was clean and transparent it was removed precipitating the silver on mossy zinc.

from the bath. While the time that the film must remain in contact with the treating bath is ROBERT L. SIBLEY. 

